1. Technical Field
The present invention relates generally to power management in processing systems, and more particularly, to a power management scheme that uses multiple time frame power measurements to estimate power consumption changes and control system power consumption.
2. Description of the Related Art
Present-day computing systems include sophisticated power-management schemes for a variety of reasons. For portable computers such as “notebook”, “laptop” and other portable units including personal digital assistants (PDAs), the primary power source is battery power. Intelligent power management extends battery life, and therefore the amount of time that a user can operate the system without connecting to a secondary source of power. Power management has also been implemented over “green systems” concerns so that power dissipated within a building is reduced for reasons of energy conservation and heat reduction.
Recently, power management has become a requirement in line power connected systems, particularly high processing power cores and systems because the components and/or systems are now designed with total potential power consumption levels that either exceed power dissipation limits of individual integrated circuits or cabinets, or the total available power supply is not designed to be adequate for operation of all units simultaneously. For example, a multiprocessing system may be designed with multiple subsystems, but have a power supply system that cannot supply the maximum potential power required by each subsystem simultaneously. In another example, a processor may be designed with multiple execution units that cannot all operate simultaneously due to either an excessive power dissipation level or a problem in distributing the requisite current level throughout the processor without excessive voltage drop. The potential power available from a power supply does not have a single value, but typically is a relationship between power level and time in which greater power is available for shorter intervals up to a maximum power level beyond which the power supply will fail at any power level (either due to protection circuitry or absolute failure such as an over-current in a voltage-regulating device).
Typically, information about changes in power consumption within a system is provided by either a static power measurement determined from current sensing and/or by thermal measurements that relate the accumulation of heat within the system to power consumption. Neither are sufficiently accurate for fine-grained power management schemes. Power management schemes requiring fine-grained power consumption information, such as that disclosed in the above-referenced patent application either measure current consumption at a fairly slow rate, or estimate power consumption based on calculations made in conformity with the power savings state of each device in the system. Current measurements lack accuracy in that they do not take into account the instantaneous voltage of the system power supply, which affects the accuracy of any power use calculation. Also, estimations based on device status are only approximations to the actual power consumed by the system. Even at the device level, the approximation is seldom accurate, as estimates of power from device or system load calculations or based on a total of activated sub-units do not accurately reflect the actual power consumption of the system. Further, the typical long term measurements made by the power subsystem are typically provided for control of thermal or current failure conditions and do not provide sufficient information for controlling short term variations in power consumption. Therefore, more power may actually be available in the short term than is actually used, or if the system is operated close to the power margin, short-term behavior may cause the system to exceed desired operating power levels.
Power supply current measurements are also generally inaccurate for the purposes of fine-grained power management. In particular, current measurements made through a small voltage drop introduced at the output of a power supply are typically difficult to calibrate accurately without interrupting the power supplied to the system.
It is therefore desirable to provide a method and system for providing power management within a processing system in response to a more accurate measurement of system and device power consumption that reflects both short term and long term constraints so that system power use may be optimized. It would further be desirable to provide a method and apparatus for calibrating the power measurement without interrupting power to the system.